Uromys (Cyromys) rex (Thomas, 1888)

Groves, C. P. & Flannery, Tim F., 1994, A revision of the genus Uromys Peters, 1867 (Muridae: Mammalia) with descriptions of two new species, Records of the Australian Museum 46 (2), pp. 145-169 : 150

Uromys (Cyromys) rex (Thomas, 1888)

Type material. HOLOTYPE, BM 88.1 .5.34, adult male skin and skull collected at Aola, Guadalcanal, Solomon Islands by C.M. Woodford.

Revised diagnosis. Larger than U. porculus but smaller than U. imperator . Differing further from U. imperator in its relatively narrower molar rows and shorter, broader skull with an especially broad, deep rostrum; its extreme development of the frontotemporal ridges; the more arched posterior nasal ends which are level with the posterior ends of the lachrymals; the absence of a post palatal spine; the very oblique ascending ramus with strongly-developed tubercle and ridges, and slender, pointed coronoid. Externally it differs in its longer tail, larger pads on the hindfeet, and larger, more rasp-like tail scales (7-9 per cm versus 9-11 per cm).

Discussion. Uromys (Cyromys) rex is the only species of U. ( Cyromys ) for which the soft palate is known ( Fig. 2 ). AM M19740 is an aged individual which shows an intriguing soft palate configuration. There are seven interdental ridges, as opposed to the five that are seen in the species of Melomys and Xenuromys . The interdental ridges are, however, irregular and incomplete. The increased number of ridges is clearly apomorphic and reminiscent of the condition of U. ( Uromys ), where between 10 and 12 interdental ridges can be present. Their irregularity and incompleteness in the only specimen of U. ( Cyromys ) thus far known, however, does not resemble the condition in U. ( Uromys ). We are unsure of how to interpret this feature. It may be pathological (the animal is extremely aged), or it may be the normal condition, in which case it must be regarded as a synapomorphy for U. ( Cyromys ) or U. rex . Within U. ( Cyromys ), U. rex is the most derived of the three species in many respects, despite its superficial resemblance to U. imperator .

The original series of seven specimens were collected at Aola by Woodford in 1887. The greater numbers of this species relative to the other two species of Uromys found on Guadalcanal by Woodford may suggest that even at this time it was the commonest taxon. It is the only one of the species of Uromys (Cyromys) to have been collected since Woodford's work. The Australian Museum holds a specimen in alcohol with the skull extracted ( AM M13594) which was collected on Guadalcanal. Unfortunately, it lacks other data. A flat skin ( AM M19739 ) belonging either to this species or U. imperator (see above, under U. imperator ) is also held in the Australian Museum. There are two specimens (skins with skulls) in the Bernice P. Bishop Museum, Honolulu, Hawaii, USA ( BBM 23988 and 24101), collected at Tabila, Guadalcanal, in June, 1964, by Peter Shanahan.

Uromys rex is still to be found on Guadalcanal, the most recent known specimen ( AM M19746) being collected by one of us ( TFF) in a relict outlier of tall rainforest in the Poha Valley north ofHoniara in 1987. It was climbing a liane high in the canopy when sighted. In its size, external morphology and habits it is convergent upon Solomys sapientis and S. salebrosus. It seems plausible that this species has been able to survive because of its arboreal habits while the terrestrial U. (C.) imperator has evidently become extinct.

Figures

Fig. 2. The soft palate of (A) Uromys caudimaculatus, (B) U. anak, (C) U. rex, (D) Xenuromys barbatus and (E) Solomys sapientis.